1. What is the diagnosis of the patient's tumor and its characteristics?
The patient's tumor was diagnosed as Epithelial Myoepithelial Carcinoma (EMCa) based on its biphasic pattern of epithelial cells and myoepithelial cells. The tumor showed myoepithelial anaplasia, nuclear atypia, and tumor-free resection margins. Immunohistochemical analysis confirmed the diagnosis, with epithelial cells showing positive for pan-cytokeratin (PAN-CK) and epithelial membrane antigen (EMA), while myoepithelial cells showed positive for P63, smooth muscle antibody (SMA), and vimentin. The tumor was a 1.6x0.8x2.4-cm, gray, solid, multinodular mass. There was no gross extraparenchymal extension, microscopic perineural tumor invasion, angiolymphatic invasion, or necrosis. The patient underwent a right total parotidectomy and peritumoral lymph node resection with facial nerve preservation, and the resected tumor was confirmed to be EMCa. The patient also developed metastatic lung nodules, which were confirmed to be metastatic EMCa through video-assisted thoracoscopic surgery and microscopic examination. Immunohistochemical analysis for androgen receptor and C-erbB2 (HER2) tests were negative, ruling out targeted therapy options. The patient received platinumbased chemotherapy, resulting in minor regression of metastatic lung nodules, but the disease was considered 'stable disease' according to the Response Evaluation Criteria in Solid Tumors (RECIST).
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2. What are the common metastasis sites in EMCa cases?
In EMCa cases, the most common metastasis sites are the lung, followed by the liver, bone, and other sites such as the brain, kidney, skin, and soft tissue. Lung metastases often co-occur with brain and bone metastasis. All metastases occur 1-28 years from the initial diagnosis. Distant metastasis leads to a poor prognosis, and aggressive tumors with solid growth pattern, nuclear atypia, DNA aneuploidy, and high proliferative activity have more aggressive progression and higher local recurrence frequency. In our case, the patient had lung metastasis with myoepithelial anaplasia and nuclear atypia, but no necrosis, angiolymphatic invasion, or positive surgical margins were observed. Regular chest CT scans are important for early detection of distant metastasis in EMCa cases.
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